Aromatic carbonate polymers exhibit excellent properties of toughness, impact resistance, heat resistance, and dimensional stability. However, in certain applications the use of aromatic carbonate polymers is limited because they exhibit environmental stress crazing and cracking. "Environmental stress crazing and cracking" refers to the type of failure which is hastened by the presence of organic solvents such as, for example, gasoline, particularly high octane no-lead gasoline, acetone, heptane and carbon tetrachloride when such solvents are in contact with parts fabricated from aromatic carbonate polymers. The most significant effect is loss of impact strength, and an increase in brittle-type failure. Contact with such organic solvents may occur, for example, when parts fabricated from aromatic carbonate polymers are used under the hood of automobiles or near the gasoline filler ports thereof, or when solvents are used to clean or degrease parts made from aromatic carbonate polymers.
Blends of polycarbonate with either polyolefin or modified polyolefin resins are well known and used in a variety of applications because inter alia of their superior impact strength compared to unblended polycarbonate resins. For example, blends of polycarbonate and a variety of polyolefin resins are described in U.S. Pat. No. 3,431,224 to Kenneth B. Goldblum. As described therein, admixtures of polycarbonate including at least one member of the class consisting of polyethylene, polypropylene, polyisobutylene, a copolymer of ethylene and an alkyl acrylate, a copolymer of ethylene and propylene, a cellulose ester, a polyamide, a polyvinyl acetal, an alkyl cellulose ether, and a polyurethane elastomer exhibit improved solvent resistance and impact strength. While the results with which additives are generally good in thick section, e.g. 6.4 mm, it has been found that there is a tendency for failure to occur with these blends after exposure to high test gasoline.
U.S. Pat. No. 4,260,693 to Ping Y. Liu described ternary polycarbonate compositions having improved impact strength. These ternary compositions comprise a mixture of an aromatic polycarbonate, an olefin-acrylate copolymer, and an acrylate copolymer. These ternary blends exhibit improved low temperature impact strength and improved aged impact strength. The olefin acrylate is ethylene ethyl acrylate 82:18 (ethylene:ethylacrylate) weight percent.
U.S. Pat. No. 4,481,331 to Ping Y. Liu discloses ternary polycarbonate compositions comprising at least one high molecular weight aromatic thermoplastic polycarbonate resin, at least one compound which is a selectively hydrogenated linear, sequential, or radial teleblock copolymer of a vinyl aromatic compound and an olefinic elastomer, and an olefin acrylate copolymer. These ternary blends exhibit improved resistance to environmental stress crazing and cracking. The same ethylene ethylacrylate is used as in U.S. Pat. No. 4,260,693. The general olefin content of the olefin acrylate is described as 70-90 weight percent.